Union types don't output correctly

[rrdelaney]

Union types don't output correctly at all in compiled JS - we need a new approach to remove the tag from a variant. Here's what I cam up with in the BS playground today:

type union_of_string_or_bool =
  | String of string
  | Bool of bool
    
type string_or_bool

external string_or_bool : union_of_string_or_bool -> string_or_bool = "Array.prototype.shift.call" [@@bs.val];;

type union_of_string_or_float =
  | String of string_or_bool
  | Float of float
    
type string_or_float

external string_or_float : union_of_string_or_float -> string_or_float = "Array.prototype.shift.call" [@@bs.val];;
    
external log : string_or_float -> unit = "" [@@bs.val "console.dir"];;

log (string_or_float (String (string_or_bool (Bool true))))

I'm pretty sure this could work, and it would cover all cases of union types.

[saschatimme]

If you could also hide the string_or_float call:

external _log : string_or_float -> unit = "" [@@bs.val "console.dir"];;
let log union_of_string_or_float = _log (string_or_float union_of_string_or_float)

log (String (string_or_bool (Bool true)))

This wouldn't cover the case of nested union, though. Do these occur at all?

[rrdelaney]

More often than I'd like them to. Another problem is when the union is declared outside of the parameter than the type is substituted